The overall goal of these studies is to evaluate the effect of the hr gene locus on immune responsiveness and tumorigenesis, utilizing congenic mouse strains. The research is divided into two areas. One area concerns evaluation of the effects of homozygosity at the hr locus in C57BL/6J mice. These studies will include determination of the effects of this gene on immune responsiveness and radiation induced leukemia susceptibility. The other area concerns identification of the lymphoid cell population(s) responsible for alterations in immune function and tumor susceptibility in HRS/J hr/hr mice. These studies will include purification of lymphoid cells and evaluation of their effectiveness in in vitro mixing and depletion experiments and in vivo adoptive transfer studies. The effects of cellular and humoral immune function will be evaluated. It is hoped that these studies will lead to a better understanding of some of the factors controlling susceptibility and resistance to cancer.